SSH via HTTP proxy

If you happen to be stuck behind a corporate firewall with only HTTP proxies for external access, you might still be able to SSH out through them using the built-in nc on *nix systems.

First, hope that the proxies haven’t disabled the CONNECT method, then simply add a section to your .ssh/config like this:

Host foobar.example.com
    ProxyCommand          nc -X connect -x proxyhost:proxyport %h %p
    ServerAliveInterval   10

This will tunnel the connection through the HTTP proxy to the remote server. The ServerAliveInterval setting is required as most proxies will drop the connection after a period of inactivity.

To avoid issues with trying to connect to the host when not behind the corporate firewall, replace the above with a fake entry for the proxy method like this:

Host foobar-proxy.example.com
    HostName              foobar.example.com
    ProxyCommand          nc -X connect -x proxyhost:proxyport %h %p
    ServerAliveInterval   10

Then use

$ ssh foobar-proxy.example.com

when inside the firewall, and

$ ssh foobar.example.com

when outside.

Simples, no external software required.